Conventional cutting shears for one-handed use are generally one size fits all. This approach may be sufficient for most people who use shears or scissors occasionally. The inexact fit of the shears or scissors with the shape and flexibility of the human hand causes limited problems.
Some portion of the population use shears or scissors in their chosen line of work, and for these people, the lack of exact fit of shears to the human hand is causing serious physical injury.
What is needed is a shear that is sized to engage the human hand to minimize stress and thus repetitive motion injuries.